Method of programming electrons onto a floating gate of a non-volatile memory cell
View Patent ↗A memory cell has a trench formed into a surface of a semiconductor substrate, and spaced apart source and drain regions with a channel region formed therebetween. The source region is formed underneath the trench, and the channel region includes a first portion extending vertically along a sidewall of the trench and a second portion extending horizontally along the substrate surface. An electrically conductive floating gate is disposed in the trench adjacent to and insulated from the channel region first portion. An electrically conductive control gate is disposed over and insulated from the channel region second portion. A block of conductive material has at least a lower portion thereof disposed in the trench adjacent to and insulated from the floating gate, and can be electrically connected to the source region. A method of programming the cell comprises the steps of creating an inversion layer in the second portion of the channel. A stream of electrons is generated at the drain region which is adjacent to the inversion layer, and the stream of electrons is passed through the inversion layer, reaching a pinch off point. The electrons are accelerated through the depletion region by the field lines from the floating gate, with little or no scattering, causing the electrons to be accelerated through the insulator, separating the floating gate from the substrate, and injected onto the floating gate.
1. In an electrically programmable and erasable memory device having a substrate of semiconductor material of a first conductivity type and having a first and second spaced-apart regions formed in the substrate of a second conductivity type, with a non-co-planar channel region formed in the substrate therebetween, wherein said non-co-planar channel region having two portions: a first portion and a second portion, an electrically conductive control gate having a portion disposed adjacent to and insulated from the first portion of the channel region for creating an inversion layer therein, a floating gate having a portion disposed adjacent to and insulated from the second portion of the channel region by an insulator, for creating a depletion region having field lines directed to the floating gate, wherein said first region is adjacent to the inversion layer, a method of programming said device comprises:
creating said inversion layer;
generating a stream of electrons at said first region and causing said stream of electrons to traverse through said inversion layer; and
accelerating said stream of electrons through said depletion region by said field lines, with little or no scattering, causing said electrons to be accelerated through said insulator and injected onto the floating gate.
2. The method of claim 1 wherein said channel region has a first portion along a horizontal surface and a second portion in a trench.
3. The method of claim 1 wherein said channel region has a first portion in a trench and a second portion along a horizontal surface.
4. The method of claim 2 wherein said first portion is substantially perpendicular to the second portion.
5. The method of claim 4 wherein said inversion layer having a pinch off point, adjacent to or in said depletion region, and wherein said stream of electrons originates at said pinch off point for acceleration through said depletion region.